Which Main Jet?

[Bilko1000]

I currently have 98 main jets with a micron exhaust and K&N air filter.

The bike will rev up to 14500 rpm in 1st 14000rpm in 2nd 13500rpm in 3rd and tends to drop revs the higher the gear. This is with the snorkel fitted to the air box. If I remove the airbox snorkel she finds it harder to accelerate, if I replace the snorkel she pulls harder.

I have the main jet needle on the third clip position and the pilot screws at 1 1/2 turns out. A friend has told me to raise the jet needle which will improve fuel flow through the main jet because the jet needle is never fully out of the main jet. I have read however that at full throttle the main jet takes over and therefore the needle clip position on the main jet needle should have no effect. Is this correct.

I am thinking I need a bigger main jet possibly a 100 or 105 size to richen the mixture at the higher rpm range. Any jetting advice together with a description of your exhaust system, air filter and whether or not the snorkel is installed would be greatly appreciated. Please also describe how your bike accelerates through the gears and at what throttle settings when replying please.

[rover220]

remove the snorkel and go for 105's. thats what mine is supposed to have (what the previous owner said and i believe it) and revs perfect apart from a little flat spot at 3-4k revs.

[Bilko1000]

Rover are u running an aftermarket exhaust and filter?

[rover220]

yes, k and n filter and micron downpipes with a striaght through micron race can

[jake]

sounds a bit weird, i would of thought it would be the same in each gear??
what does it do when it gets there? whats it sound like?
I dont think the micron pipework makes a lot of difference to flow, unless you have cut the baffles out?

ive heard that the k and n's work better with snorkle off on the l airbox, im not familiar with the L's bits tho.

Ive got 102 mains on mine. beet system, ramair/no filter. I block the aircorrector jets tho, and would be better with 100 mains, as running slightly rich last run. Also be aware the dynojet and keihin jets are different sizes. I also have my aircorrector screws out 3 turns. dynojet needles on full height

edit, just thought if its 'cackling' if you get me, up high revs, make sure you aint got an air leak, carb rubbers or anywhere around the back of the box. I forgot to put the access bungs back in once on a standard airbox, and it stuttered away at around 10k

[Bilko1000]

Thanks Jake, Its not stuttering at all its just slowly climbing up to a maximum amount of revs and then staying there. If I place the snorkel on the air box it revs better. I just think the bike is not getting enough fuel at the higher rev range. Ive ordered 105 main jets and I will lower the main needles down to the 2nd position and see how she runs. I will also remove the snorkel which should hopefully cure the problem.

Can you tell me though how do you block the aircorrector jets? When you mean dynojets on full height do you mean the 1st leanest clip position or the last richest clip position?

[MillaMeter]

Hi,

Try checking the spark plugs to see whether the bike is running rich or lean. I'm guessing your bike is running lean, try turning your pilot screws out half a turn.

Regards

Rich

[jake]

hi mate.
i mean the leanest setting, the first notch down.
we did a back to back test on the dyno with 3 different needles. J1, h2 and the dynojet ones.
I was trying to lean it out, especially in the middle, as most do run rich standard.
the dynojet gave the best curve, but the j1 leaned it right up the top nicely.. i went with the dynojets.
The aircorrector jets, if you look at the mouth of your carbs fitted to the bike, if you where sitting on the bike. They are the jets closest to you.
Its a tuners trick to block them apparantley, otherwise, im told, you have to use big mains jets which can cause over fueling probs. I block them with a bit of silicone..but i think dynojet sell a closed end jet.

the adjuster screws dont really effect the fueling above 3k to much, i just use them to set the idle, if it bogs or hangs.

Im in no way an expert tho mate, i only got back into 400's last year with racing, so have been fiddling with them since.
where in the country are you?

edit. id leave the needles on full height, try them 105 without blocking the aircorrectors, see what she does, and go from there..

[Bilko1000]

Thanks for your replies.

She was running too lean at the top end with the micron exhaust system and the K&N Filter. I took Rover 220's advice and fitted 105 Main Jets replacing the 98 standard. I also leaned out the
mid range by placing he needle clip on the 1st setting so the needle is at its longest, leanest setting. It worked, my mid range is just right not rich or lean, the engine is cool and I can now
rev to the red line as the engine is getting enough fuel to mix with the air at high speed. Thanks for all your replies. My idle screws are 11/2 turns out. The bike really runs now and feels as
quick as my 600 around 10,000 revs to the redline very impressive for a 400cc.

[cmforse]

Hi all

Many posts refer to needle adjustment - clips in grooves etc.

As far as I can see from the manual and our bike, the stock needles are not adjustable - they sit flat on the slide. One could shim them up I guess, but seems a "bodge" !

Are you all referring to Dynojet needles ??


Second question - what is your experience with the Dynojet kits - seems to be mixed experiences, are they worth the spend, how well do they work "out of the box" ??


Cheers

Charles

[zimm]

they seem to work, but i wouldnt pay for one new .. and the only part of the kit worth getting is the adjustable needles, as any dyno shop will have the jets sat there, and getting it set on a dyno is what you ought to be doing.

shimming needles is acceptable, but as jake said zxr's tend to be rich there anyway (depending on spec) so you'd only make it worse ..

if running a stock exhaust dont bother, same with the KnN filter tbh .. even with a race system .. there's no real benefit to running it ..

I fitted a KnN, dynojet kit and micron system to my L (its rover220's now) (got the kit and KnN second-hand) it sounds better and revs cleanly but its a lot of money and hassle for an extra 2-3 bhp and a different noise..

as a comparison, my H1 has completely stock carbs, stock filter, and modified (de-baffled) exhaust, .. all i'd consider doing is maybe upping the main jets to #100's over the #98's .. and thats only because i have some in a pot.. i certainly wouldnt go out and pay for some.